If someone spoke to you and didn't annunciate their words properly, you'd ask them to repeat themselves until you understood. Similarly, when someone types like a berk, you have to spend more time rereading it so you understand it as it is meant to be.
The difference being you might be able to persuade someone to pronounce something clearer by getting them to repeat it, whereas re-reading a shit post doesn't get any easier.
I suppose this applies more to text talk, but if someone writes a post with no punctuation you can sometimes misinterpret it.